Shallow Juan de Fuca slab may boost shaking in future Cascadia quake
New seismic data show the Juan de Fuca plate under northern Oregon is about 5 km shallower than thought, potentially raising ground shaking by up to 17 % and highlighting a deep basin near Tillamook that could further amplify tremors.
A recent seismic investigation reveals that the Juan de Fuca plate subducting beneath northern Oregon is about 20 km deep near the shoreline, roughly 5 km shallower than previous estimates. This shallower interface could boost shaking intensity from a future Cascadia megathrust event by approximately 9 to 17 % along the coast. In addition, scientists detected a deep sedimentary basin beneath Tillamook, a structure that can trap seismic energy and prolong strong motions, especially affecting tall buildings.
The results stem from an array of 192 temporary nodal seismometers installed during the summers of 2021 and 2022, combined with offshore seismic records spanning Vancouver Island to northern California. The combined datasets provide a more detailed picture of the subduction zone, addressing the scarcity of local earthquakes that has limited prior research. The team plans to apply the same methodology to investigate the Tualatin Basin near Portland. These insights aim to refine earthquake hazard assessments for populated areas of northern Oregon.
Why it matters
Understanding a shallower slab and basin effects can improve quake-risk forecasts for communities along Oregon's coast.
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